This invention relates to improvements in a control system for an electromagnetic actuator, and more particularly to the control system for the electromagnetic actuator of the type having two electromagnets and an armature whose position is freely changeable upon receiving attraction force from each electromagnet.
As intake and exhaust valves of a vehicular internal combustion engine, electromagnetically actuated valves (valves actuated by electromagnetic actuators) have been proposed to be used in place of conventional valves driven by a cam mechanism. The electromagnetically actuated valves not only can render the cam mechanism unnecessary but also can readily optimize opening and closing timings of the intake and exhaust valves in accordance with operational condition of the engine, thereby improving power output and fuel economy of the engine.
A typical example of such an electromagnetically actuated valve is disclosed in Japanese Provisional Publication No. 8-170509, in which an engine valve (intake or exhaust valve) is connected to an armature movably disposed between an opening-side electromagnet for opening the valve and a closing-side electromagnet for closing the valve; the valve being normally biased to a position at which the valve is partially opened, under a biasing force of a pair of springs. Before engine starting, the opening-side and closing-side electromagnets are alternately energized to apply electromagnetic forces to the armature to make vibration resonance of the armature, under action of the springs, and thereby increase vibration amplitude of the armature. Then, initialization is carried out to keep the armature at an opening position for opening the valve and a closing position for closing the valve. Thereafter, when the valve is to be changed from its closed state to its opened state, current supply to the closing-side electromagnet is interrupted so that the valve and the armature are moved under the bias of the springs. Then, at a timing at which the armature approaches the opening-side electromagnet, current supply to the opening-side electromagnet is initiated to attract the armature thereby opening the valve. A similar operation is made also when the valve is to be changed from the opened state to the closed state. In this arrangement, current supply to the electromagnet is initiated at the timing at which the armature approaches the electromagnet. Consequently, this arrangement can reduce an electromagnetic force required for the electromagnet, thereby reducing the size of a driving device for the valve.
Additionally, it has been also proposed that an amount of current to be supplied to an electromagnet is variable in accordance with the position of an armature in order to decrease the velocity of the armature when the armature is attracted to the electromagnet. This reduces collision noise of the armature and ensures the durability of an electromagnetic actuator for an engine valve. This technique is disclosed in earlier Japanese Patent Application No. 11-355106 having inventors including the inventors of the present application. The Japanese Patent Application is based on Japanese Patent Application No. 10-359591 which was abandoned.
Drawbacks have been encountered in the internal combustion engines provided with the above conventional electromagnetically actuated valves, as set forth below. That is, when, for example, misfire occurs in the engine so that pressure within an engine cylinder (to be applied to the valve) is sharply lowered, a driving force required for opening the valve is reduced and therefore a moving velocity of the valve and the armature connected to the valve becomes excessively large under the biasing force of the springs upon interruption of current supply to the closing-side electromagnet. This renders the velocity of the armature excessively large relative to the target velocity when current supply to the opening-side electromagnet is initiated, so that the control system for the electromagnetically actuated valves becomes out of control.
If the control system becomes out of control, the valve is unavoidably kept partially open and kept at a neutral position. Therefore, exhaust gas will be transferred to the intake side while exhaust gas in the engine cylinder, generated during the misfire, will be transferred to the intake sides of other engine cylinders through the intake valves thereby affecting combustion in other engine cylinders. Additionally, after the valve has been kept at its neutral position, torque cannot be generated in the misfired engine cylinder until an initialization under the above-mentioned vibration resonance has been accomplished.
Furthermore, when the neutral position of the valve is shifted, for example, owing to the lack of uniformity in the biasing force of each spring and the change in the biasing force of the springs upon lapse of time (other than the above-discussed misfire), the moving velocity of the valve becomes too high thereby causing problems similar to those previously discussed.
Therefore, it is an object of the present invention to provide an improved control system for an electromagnetic actuator, which can effectively overcome drawbacks encountered in the conventional similar techniques.
Another object of the present invention is to provide an improved control system for an electromagnetic actuator, which can reduce collision noise of an armature while ensuring a high response characteristics of the actuator, and ensure a high durability of a movable section (including the armature) and electromagnets.
A further object of the present invention is to provide an improved control system for an electromagnetic actuator, which can prevent the moving velocity of an armature from becoming excessively large under biasing force of springs, thereby accomplishing stable control for changing position of the armature between two electromagnets.
An aspect of the present invention resides in a control system for an electromagnetic actuator including first and second electromagnets each of which develops an electromagnetic attraction force upon supply of current thereto, the electromagnetic attraction force changing in accordance with an amount of current to be supplied thereto; an armature disposed to be attractable to one of the first and second electromagnets under the electromagnetic attraction force; and a spring for developing biasing force for biasing the armature to be put at a neutral position between the first and second electromagnet. The control system comprises a control circuit programmed to carry out (a) decreasing the amount of current to be supplied to the first electromagnet and controlling the amount of current to be supplied to the first electromagnet so as to restrict a moving velocity of the armature, at a first stage in a course of changing the armature from a first position at which the armature is kept attracted to the first electromagnet to a second position at which the armature is kept attracted to the second electromagnet; and (b) initiating supply of current to the second electromagnet at a timing at which the armature approaches the second electromagnet upon the biasing force of the spring so as to attract the armature to be kept at the second position, at a second stage in the course of changing the armature from the first position to the second position, the second stage being after the first stage.
Another aspect of the present invention resides in a control system for an electromagnetically actuated valve. The control system comprises first and second electromagnets each of which develops an electromagnetic attraction force upon supply of current thereto. The electromagnetic attraction force changes in accordance with an amount of current to be supplied thereto. An armature is disposed to be attractable to one of the first and second electromagnets under the electromagnetic attraction force. The armature is connected to the electromagnetically actuated valve. A spring is provided for developing biasing force for biasing the armature to be put at a neutral position between the first and second electromagnet. The control system comprises a control circuit programmed to carry out (a) decreasing the amount of current to be supplied to the first electromagnet and controlling the amount of current to be supplied to the first electromagnet so as to restrict a moving velocity of the armature, at a first stage in a course of changing the armature from a first position at which the armature is kept attracted to the first electromagnet to a second position at which the armature is kept attracted to the second electromagnet; and (b) initiating supply of current to the second electromagnet at a timing at which the armature approaches the second electromagnet upon the biasing force of the spring so as to attract the armature to be kept at the second position, at a second stage in the course of changing the armature from the first position to the second position, the second stage being after the first stage.
A further aspect of the present invention resides in a method of controlling an electromagnetic actuator including first and second electromagnets each of which develops an electromagnetic attraction force upon supply of current thereto, the electromagnetic attraction force changing in accordance with an amount of current to be supplied thereto; an armature disposed to be attractable to one of the first and second electromagnets under the electromagnetic attraction force; and a spring for developing biasing force for biasing the armature to be put at a neutral position between the first and second electromagnet. The method comprises (a) decreasing the amount of current to be supplied to the first electromagnet and controlling the amount of current to be supplied to the first electromagnet so as to restrict a moving velocity of the armature, at a first stage in a course of changing the armature from a first position at which the armature is kept attracted to the first electromagnet to a second position at which the armature is kept attracted to the second electromagnet; and (b) initiating supply of current to the second electromagnet at a timing at which the armature approaches the second electromagnet upon the biasing force of the spring so as to attract the armature to be kept at the second position, at a second stage in the course of changing the armature from the first position to the second position, the second stage being after the first stage.